Explanation: The Crab Nebula is cataloged as M1, the first on Charles Messier's famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second. Over the past decade, its expansion has been documented in this stunning time-lapse movie. In each year from 2008 to 2017, an image was produced with the same telescope and camera from a remote observatory in Austria. Combined in the time-lapse movie, the 10 images represent 32 hours of total integration time. The sharp, processed frames even reveal the dynamic energetic emission within the incredible expanding Crab. The Crab Nebula lies about 6,500 light-years away in the constellation Taurus.

[url][/url]That is indeed a stunning time-lapse movie of the Crab Nebula.

I was aware that the network of red Hα filaments was expanding, because stills taken several years apart had demonstrated the expansion. What the movie shows, however, is that most of the outward motion seems to take place in the white synchrotron radiation.

My interest in synchrotron radiation is minimal, but this is what Wikipedia says:

Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when charged particles are accelerated radially, i.e., when they are subject to an acceleration perpendicular to their velocity (a ⊥ v)....Synchrotron radiation is also generated by astronomical objects, typically where relativistic electrons spiral (and hence change velocity) through magnetic fields. Two of its characteristics include non-thermal power-law spectra, and polarization....A class of astronomical sources where synchrotron emission is important is the pulsar wind nebulae, a.k.a. plerions, of which the Crab nebula and its associated pulsar are archetypal. Pulsed emission gamma-ray radiation from the Crab has recently been observed up to ≥25 GeV,[11] probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab[12] at energies from 0.1 to 1.0 MeV illustrates a typical synchrotron radiation.

I only understood parts of that, but never mind. A more interesting question is, is the white synchrotron radiation really pushing the nebula outwards, thus making it expand? Or maybe the synchrotron radiation has little to do with the expansion, and it is instead the jets that are responsible for that? But why don't the jets "punch holes" in the nebula and make it all drain away like water in a drain? Is it because the electrons are trapped in the magnetic field of the pulsar?

As a color commentator, I am of course interested in the color of the nebula. In today's APOD it looks like a very tattered Danish flag, which is red and white. Tiny shreds of the green pale of the Italien flag can be spotted at the "bottom" of the nebula.

I have to wonder why there is so much ionized hydrogen glowing red in the nebula, and so little oxygen glowing green. I thought there was quite a lot of oxygen in the supernova remnants of massive stars.

Ann wrote:[url][/url]That is indeed a stunning time-lapse movie of the Crab Nebula.

I was aware that the network of red Hα filaments was expanding, because stills taken several years apart had demonstrated the expansion. What the movie shows, however, is that most of the outward motion seems to take place in the white synchrotron radiation.

My interest in synchrotron radiation is minimal, but this is what Wikipedia says:

Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when charged particles are accelerated radially, i.e., when they are subject to an acceleration perpendicular to their velocity (a ⊥ v)....Synchrotron radiation is also generated by astronomical objects, typically where relativistic electrons spiral (and hence change velocity) through magnetic fields. Two of its characteristics include non-thermal power-law spectra, and polarization....A class of astronomical sources where synchrotron emission is important is the pulsar wind nebulae, a.k.a. plerions, of which the Crab nebula and its associated pulsar are archetypal. Pulsed emission gamma-ray radiation from the Crab has recently been observed up to ≥25 GeV,[11] probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab[12] at energies from 0.1 to 1.0 MeV illustrates a typical synchrotron radiation.

I only understood parts of that, but never mind. A more interesting question is, is the white synchrotron radiation really pushing the nebula outwards, thus making it expand? Or maybe the synchrotron radiation has little to do with the expansion, and it is instead the jets that are responsible for that? But why don't the jets "punch holes" in the nebula and make it all drain away like water in a drain? Is it because the electrons are trapped in the magnetic field of the pulsar?

As a color commentator, I am of course interested in the color of the nebula. In today's APOD it looks like a very tattered Danish flag, which is red and white. Tiny shreds of the green pale of the Italien flag can be spotted at the "bottom" of the nebula.

I have to wonder why there is so much ionized hydrogen glowing red in the nebula, and so little oxygen glowing green. I thought there was quite a lot of oxygen in the supernova remnants of massive stars.

Ann, In your link to the nebula, the Synchrotron Radiation is in the blue, the blue in the CENTRAL AREA, but there is also MUCH Oxygen indicated, in the last paragraph...TODAY'S image I think uses different filters, or color scheme, so it may not seem like there is much...details, details... Boomer12k hopes his friend is having a great New Years Week!!!!

Ann wrote:... [I]s the white synchrotron radiation really pushing the nebula outwards, thus making it expand? Or maybe the synchrotron radiation has little to do with the expansion, and it is instead the jets that are responsible for that? ...

The nebula is expanding due to the kinetic energy the gas got in the supernova explosion. The emissions from the pulsar are at most a very minor contribution to that expansion. Think of what happens when there is an explosion here on the Earth: Stuff is thrown out every which way. On Earth, the outward expansion of the gas from an explosion is stopped by the atmosphere: As the explosion gases expand, their pressure drops. And once the pressure become the same as that of the atmosphere, the expansion stops.

In space, there is no atmosphere, and those gases got thrown out at much higher speeds that a conventional explosion. (A supernova is a star going off like an oversized nuclear bomb after all.) So the gases from the explosion will expand for a very long time, and not stop until it pressure becomes as low as that of the interstellar medium, which is almost a vacuum. If fact, the Veil Nebula is part of the remnant from a supernova than occurred over 7,000 years ago, and which is still expanding.

ems57fcva wrote:In space, there is no atmosphere, and those gases got thrown out at much higher speeds that a conventional explosion. (A supernova is a star going off like an oversized nuclear bomb after all.) So the gases from the explosion will expand for a very long time, and not stop until it pressure becomes as low as that of the interstellar medium, which is almost a vacuum. If fact, the Veil Nebula is part of the remnant from a supernova than occurred over 7,000 years ago, and which is still expanding.

The interstellar medium has a density ~ 1 atom/cm3

Atoms have a collision cross-section of ~ 10-16 cm2/atom

Hence the mean free path ~ 1016 cm = 1011 km ~ 0.01 light years.

After the gases from the supernova have traveled ~10 light years (~ 1,000 mean free paths)they will have swept up ~1,000 times their own mass in interstellar mediumand slowed to ~0.001 times their initial velocity (; momentum being conserved).

Each time i see this image, I wonder the visual-meaning of the ripples and the stone-in-the-pond effect we see into the movie.I refer to the "waves" we see in the gas around the pulsar... I sometimes explained it to myself (as a rookie) like "waves of density" of the expanding gas, butcould it be also a sign of the space-time deformation due to the central neutron star, which is spinning at relativistic speeds?

distefanom wrote:Each time i see this image, I wonder the visual-meaning of the ripples and the stone-in-the-pond effect we see into the movie.I refer to the "waves" we see in the gas around the pulsar... I sometimes explained it to myself (as a rookie) like "waves of density" of the expanding gas, butcould it be also a sign of the space-time deformation due to the central neutron star, which is spinning at relativistic speeds?

No. Such effects are incredibly tiny- that's why we need gravitational wave telescopes to detect them. They aren't large enough to produce visible effects like that.

The Crab sure seems fascinating. It would have begun as a point (from the view of Earth) in 1054, when we saw first light of the explosion. I was not able to figure out from the Wikipedia articles whether or not it is known what type of supernova was involved (perhaps I did not read them patiently enough). The remnant includes a pulsar which the articles said is a neutron star.

Art described the slowing of the ejected mass above. I don't know how much confidence he has in the various parameters for his estimate.

In 2007 the Crab pulsar had a period of 0.0331 sec and a period derivative of 4.22×10-13s/s.

I wonder how long of a time period for observation was necessary to determine this derivative. Perhaps there is some clever way to do it in a short period of time rather than what would be my first idea of trying to measure the period more or less directly once each year. For such a derivative, one would expect after about 10 years (= 3.15576 E+08 sec) that the rate would slow from 0.0331 sec to 0.03296 sec. Long-term, it seems there's not much chance it would be a linear process, so the derivative would change. Does this sound correct? I gather that a typical pulsar spin-down is a very long process, so it's not like this pulsar will go quiet any time soon.

MarkBour wrote:The Crab sure seems fascinating. It would have begun as a point (from the view of Earth) in 1054, when we saw first light of the explosion. I was not able to figure out from the Wikipedia articles whether or not it is known what type of supernova was involved (perhaps I did not read them patiently enough). The remnant includes a pulsar which the articles said is a neutron star.

Art described the slowing of the ejected mass above. I don't know how much confidence he has in the various parameters for his estimate.

In 2007 the Crab pulsar had a period of 0.0331 sec and a period derivative of 4.22×10-13s/s.

I wonder how long of a time period for observation was necessary to determine this derivative. Perhaps there is some clever way to do it in a short period of time rather than what would be my first idea of trying to measure the period more or less directly once each year. For such a derivative, one would expect after about 10 years (= 3.15576 E+08 sec) that the rate would slow from 0.0331 sec to 0.03296 sec. Long-term, it seems there's not much chance it would be a linear process, so the derivative would change. Does this sound correct? I gather that a typical pulsar spin-down is a very long process, so it's not like this pulsar will go quiet any time soon.

I'll leave all the clever math questions for Art and the other math whizzes to answer, but I can tell you what kind of a supernova it was. It was a massive star undergoing core collapse, although I can't tell you if it was a type II, type Ib or one of the other core collapse supernovas.

Massive stars undergoing core collapse are the only ones leaving neutron stars, pulsars and magnetars behind, to the best of our understanding.

Ann

Edit: I love that particular song and scene from Sound of Music (I can do without some of the others)!